Ultra-fine grain materials have attracted the attention of many researchers due to their unique mechanical properties. Control of grain size and texture are known as one of the most effective ways to achieve desired material properties. Severe plastic deformation (SPD) processes are commonly used methods for grain refinement of metallic materials, although they have not been well received by industry. The most important limitations of introduced methods are the small size of the product and the large number of steps needed to reach the desired texture. In recent years, various SPD methods for improving texture and grain size of bars with small diameters are provided. However, imposing large plastic strain to small diameter wires is a complex process and technically challenging. Traditionally, wires are made by drawing; imposing sever plastic deformation to wires with small diameter is a complex process.
Enhancing mechanical properties of wires during fabrication is highly desirable for the production of high strength, durable, and ductile wires. Several methods have been proposed over the years for the improvement of the mechanical properties of wires. For example, severe plastic deformation (SPD) methods for fabricating nano-structured materials have been used with positive results. However, metal wires fabricated from such methods suffer from low ductility due to lack of work hardening.
It has been shown that one of the possible solutions to tackle this problem is to introduce non-uniform grain structure, i.e., mixture of both fine grains (to improve strength) and coarse grains to keep reasonable ductility level. An apparatus, which produces a non-uniform grain structure in the fabricated wire, is required. Furthermore, in other existing SPD methods for fabricating wires with small cross section, each method has some disadvantages such as the limited length of the final product, low speed, low production rate, etc. An apparatus or a method, which has the ability to impose continuous plastic deformation to wires with acceptable speed and high production rate is required.
Conventionally, most of the severe plastic deformation (SPD) methods use a die with an intersection angle to impose a plastic shear strain to the raw materials. In these processes, the amount of achievable plastic strain is limited with respect to the die angle. In order to attain a higher level of plastic strain the intersection angle of a die should be decreased. However, in practice, the use of intersection angles less than 90° is difficult. An apparatus or method, which is capable of achieving the highest level of plastic strain, is required. Moreover, an apparatus which produces a continuous torsion deformation to a wire with diameter below 4 mm, is required.
There is a long felt but unresolved need for an apparatus, which produces a non-uniform grain structure in the fabricated wire. Moreover, there is a need for an apparatus or a method, which has the ability to impose continuous plastic deformation to wires with acceptable speed and high production rate. Furthermore, there is a need for an apparatus or method, which is capable of achieving the highest level of plastic strain. Additionally, there is a need for an apparatus, which produces a continuous torsion deformation to a wire with diameter below 4 mm.